Some semiconductor processes use tetraethylorthosilicate (TEOS) or other volatile compounds that are liquid at room temperature and pressure. TEOS is commonly supplied to a semiconductor process chamber for the deposition of thin films of silicon dioxide (SiO2) on semiconductor substrates using a chemical vapour deposition (CVD) process. Within the process chamber, the TEOS dissociates in the presence of an oxygen source to form SiO2, which deposits on the substrate within the chamber. Depending on the flow rate of the gaseous TEOS to the chamber, a waste stream drawn from the chamber by a vacuum pumping arrangement typically contains unconsumed TEOS, as well as by-products from the process within the chamber.
The discharge of gaseous TEOS from the process chamber can lead to uncontrolled TEOS condensation downstream from the chamber exhaust, for example due to insufficient purging with relatively inert gas such as N2, or due to a relatively low temperature within the exhaust line from the process chamber. The random accumulation of pools of volatile liquid TEOS within the pumping arrangement can present a safety hazard, as they may react strongly with other species subsequently introduced to the process chamber, for example fluorine for chamber cleaning, and with air leaking into the pumping arrangement. Such accumulation of liquid TEOS within the pumping arrangement can also occur in the event that the process tool discharges liquid TEOS directly to the process chamber or foreline.
An abatement device is typically provided downstream from the process chamber for removing TEOS from the waste stream before it is exhausted into the atmosphere. Random accumulation of liquid within the pumping arrangement conveying the gas stream from the process chamber to the abatement device can lead to large fluctuations in the gas flow entering the abatement device, which can be detrimental to the efficiency of the waste stream abatement.
It is an aim of at least the preferred embodiments of the present invention to seek to solve these and other problems.